Engines having an overhead camshaft arrangement include at least one camshaft that is connected to the cylinder head. Cylinder heads for overhead camshaft engines include integral posts (or other similar structures) with semi-circular bearing surfaces to support and connect the camshaft to the cylinder head. These integral posts may extend beyond the top deck surface of the cylinder head where the valve cover is attached to the cylinder head. To connect a camshaft to a cylinder head, the camshaft is situated in the cylinder head so that the bearings of the camshaft are positioned in the semi-circular bearing surfaces of the integral posts of the cylinder head. Cam caps, also having semi-circular bearing surfaces, are placed over the bearings of the camshaft and are connected to the integral posts of the cylinder head. Once the cam caps are attached, the semi-circular bearing surfaces of the integral posts and the semi-circular bearing surfaces of the cam caps form a camshaft bore that completely surrounds the bearings of the camshaft, and the camshaft is thus securely attached to the cylinder head.
Machining the camshaft bore presently requires large and expensive equipment. This is because the cam caps are mounted to a cylinder head or cylinder head casting and then an expensive drill tool having a large drill bit is used to precision-machine the bores between the cam caps and the integral posts on the cylinder head.
In an operating engine, a cylinder head is exposed to harsh conditions including heat created by combustion and friction, as well as wear and tear caused by the many moving valvetrain components. Under these harsh conditions, the cylinder head may become deformed, cracked, or otherwise damaged. For example, the bearing surfaces on the integral posts and cam caps may become gouged if these pieces are not properly lubricated. If the integral posts which support the camshaft (including the bearing surfaces) are damaged, the rotation of the camshaft is likely to be impacted, which can result in diminished performance of the engine or possibly damage to other engine components. Although the integral posts of a cylinder head are only a small portion of the entire cylinder head, damage to these integral posts often requires that the entire cylinder head be replaced.
In addition to replacing cylinder heads when they are damaged, automotive enthusiasts often replace or modify existing valvetrain components to improve the performance of an engine. For example, installing after-market camshafts with specially designed cam lobes is a popular way to improve an engine's horsepower and torque profile. Thus, automotive enthusiasts prefer modular components which may be installed, removed, or changed as desired.
Accordingly, a need exists in the art for a replaceable and serviceable cam journal which connects a camshaft to a cylinder head.